Convex lens of 10 cm focal length is combined with a concave lens of 6 cm focal length. Find the focal length of the combination.
Correct answer: B. - 15 cm
- A. 15 cm
- B. - 15 cm
- C. 30 cm
- D. - 30 cm
Explanation
When combining lenses, the focal length of the combination is calculated using the formula 1/f = 1/f1 + 1/f2. In this case, the focal lengths of the convex and concave lenses are +10 cm and -6 cm respectively. Plugging these values into the formula, we get 1/f = 1/10 + 1/-6, which results in f = -15 cm. This negative sign indicates that the combination acts as a diverging lens.The other options are incorrect because they do not consider the signs of the focal lengths when combining lenses, leading to miscalculations.
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Light is studied through reflection, refraction, dispersion, interference, diffraction and polarization, linking ray behavior with its wave nature. Questions may involve mirrors, lenses, optical instruments, refractive index and image formation, while geometrical optics deals with rays and wave optics explains effects such as interference and diffraction.
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